The proposed research will investigate in depth the brain stem connections of the cat superior colliculus. This will be accomplished by using recently developed neuroanatomical methods particularly suited for the detailed analysis of the origin, course, and termination of these projections; namely, the autoradiographic tracing method and the retrograde method utilizing horseradish peroxidase. The projections will be studied in both the transverse and horizontal planes and the results will be charted with the highly accurate recording capabilities of an electronic X-Y pantograph system. This project will be broken down into the studies of the following projection systems: 1) the intertectal connection, 2) the predorsal bundle, and 3) the tectoreticular and tectopontine projection. In each study special consideration will be given to identifying the exact site of origin of the projection, to exploring for yet unknown projections, and to reevaluating previously described projections. Our primary concern, however, will be to investigate the possible topographic organization of these projections. The findings of this research will be evaluated in the light of the functional organization of the tectum.